Hanger device useful in forming concrete structural slabs

ABSTRACT

A hanger device useful in conjunction with temporary decking or forms for pouring concrete structural slabs, such as roofs or floors, is constructed of a channel bearing a curved, pivoting tongue-shaped member. The channel is adapted to hold a joist for supporting the temporary decks on which the concrete is poured. The tongue-shaped member protrudes upwardly through a slot in the top of the channel and rests at its downwardly curved end on a preformed support, such as a joist or beam. Rotational movement of the tongue-shaped member is prevented by a locking pin cooperating therewith. In forming the slab, the poured concrete covers the protruding portion of the tongue-shaped member, the preformed support and the form decking. After hardening of the concrete, the hanger device carrying the supporting joist is readily removed by withdrawing the locking pin and applying a downward force on the channel is the vicinity of the tongue shaped member, resulting in a slight vertical displacement of the tongue-shaped member from the concrete contiguous thereto and rotation thereof out of the concrete without binding. The device may then be reused in forming another slab.

United States Patent Martin 51 3,693,929 [4 1 Sept. 26, 1972 [54] HANGERDEVICE USEFUL IN FORMING CONCRETE STRUCTURAL SLABS [72] Inventor: SidneyL. Martin, 6520 S.W. 79th Court, Miami, Fla. 33143 [22] Filed: Jan. 18,197 1 211 App]. No.: 107,059

Related US. Application Data [63] Continuation-in-part of Ser. No.850,735, Aug.

18, 1969, abandoned.

[52] US. Cl ..249/25 [51] Int. Cl ..E04g 11/38 [58] Field of Search..249/23-25, 28

[56] References Cited UNITED STATES PATENTS 583,099 5/1897 Tompkins..249/25 1,779,735 10/1930 Harm ..249/25 1,186,614' 6/1916 Smith..249/25 2,012,616 8/1935 Miller ..249/25 FOREIGN PATENTS ORAPPLICATIONS 428,208 5/1935 Great Britain ..249/23 Primary Examinerl.Spencer Overholser Assistant Examiner-Ben D. Tobor AttorneyMeyerNeishloss and Alvin E. Ring 5 7 ABSTRACT A hanger device useful inconjunction with temporary decking or forms for pouring concretestructural slabs, such as roofs or floors, is constructed of a channelbearing a curved, pivoting tongue-shaped member. The channel is adaptedto hold a joist for supporting the temporary decks on which the concreteis poured. The tongue-shaped member protrudes upwardly through a slot inthe top of the channel and rests at its downwardly curved end on apreformed support, such as a joist or beam. Rotational movement of thetongue-shaped member is prevented by a locking pin cooperatingtherewith. In forming the slab, the poured concrete covers theprotruding portion of the tongueshaped member, the preformed support andthe form decking. After hardening of the concrete, the hanger devicecarrying the supporting joist is readily removed by withdrawing thelocking pin and applying a downward force on the channel is the vicinityof the tongue shaped member, resulting in a slight vertical displacementof the tongue-shaped member from the concrete contiguous thereto androtation thereof out of the concrete without binding. The device maythen be reused in forming another slab.

PATENTEBWB I912 3.693.929

SHEET 2 OF 2 //WA/mQ. S/DA/EY 4. MART/N HANGER DEVICE USEFUL IN FORMINGCONCRETE STRUCTURAL SLABS This application is a continuation-in-part ofmy copending application, Ser. No. 850,735, filed Aug. 18, 1969, nowabandoned.

SUMMARY OF THE INVENTION This invention relates to a hanger deviceuseful in forming substantially horizontal concrete structural slabs,such as floors and roofs. More particularly, it comprises support meanshaving inner and outer surfaces, such as an inverted channel or arectangular or tubular conduit, adapted to hold a joist for supportingtemporary forms or decks for the concrete and carrying a movabletongue-shaped member protruding above and below the top of the supportmeans through a slot adjacent one end thereof. The portion of thetongueshaped member protruding above the support means is curved,defines an arc which is substantially a segment of the circumference ofa circle, and is adapted to rest at its downwardly curved end on apreformed support for the concrete slab. The device is provided withlocking means preventing rotational movement of the tongue-shaped memberduring pouring of the concrete while the curved end of the member isresting on the preformed support and is being covered by the concrete. Acircular pivot means is fixed to the portion of the tongue-shaped memberwithin the support means immediately adjacent the slot and interiorly ofthe tongue-shaped member. The pivot means cooperates with thetongue-shaped member to rotate the member free of the hardened concretewithout binding upon removal of the locking means.

THE DRAWINGS In the drawings FIG. 1 is a plan view of the hanger deviceof the invention;

FIG. 2 is a side elevation of the device of FIG. 1;

FIG. 3 is a front elevation of the device shown in FIGS. I and 2;

FIG. 4 is a view, partly in section, taken along the line IV-IV of FIG.3 in the direction of the arrows;

FIG. 5 is a view similar to that of FIG. 4 showing withdrawal of thehanger device and its tongue-shaped member from a hardened concreteslab; and

FIG. 6 is a fragmentary perspective view showing the hanger device andaccompanying form joists and decking in position for pouring a concretestructural slab.

DETAILED DESCRIPTION Referring to the drawings, the hanger device of theinvention comprises a support means having inner and outer surfaces,such as the inverted channel shown generally at 10. The inverted channelhas a top portion 11 and side portions 12. Typically, the channel can bemade of A: inch steel and can have a length of about 14 inches, bothdimensions depending upon the load to be carried The interior of thechannel may be shaped to fit over the ends of wood joists 13, forexample, 2 X 6 or 2 X 8 inch joists, or the ends of suitable steeljoists (not shown) which support the form decks or decking 14 on which aconcrete slab is to be formed.

,. the inner surface of the top 11 of the inverted channel to thesurface of the clamping plate may be varied to accommodate theparticular size of joist being used.

Adjacent that end of the channel to which the joist is fastened, thereis provided a movable tongue-shaped member 19 which is adapted to restor bear at its downwardly curved end 20 on a preformed support 21 forthe concrete slab 22. The preformed support can be a flush-sidedconcrete beam or a steel beam having projecting flanges, such as anl-beam. As best shown in FIGS. 1 and 4, the tongue-shaped memberprotrudes above and below the top of the channel through a slot 23 in acontinuation 24 of the top 11 of channel 10. As will be described later,the continuation 24 also forms part of a hanger device spacing assemblywhich is attached to the sides of the inverted channel.

The portion of the tongue-shaped member 19 protruding above the channeldefines an are which is substantially a segment of the circumference ofa circle, as shown in FIGS. 2 and 4. A substantially vertical positionlimiting lug 26 is fixedly secured, as by welding, at position 27 on theinner (concave) surface of the curved protruding portion of thetongue-shaped member 19 approximately midway of the horizontal distancebetween the slot 23 and the end 20 of the tongue-shaped member. Anintegral continuation 26a of lug 26 is also welded to the lower end 28of the portion of the tongue-shaped member terminating within theinverted channel 10. The position 27 at which the limiting lug is weldedto the member 19 is not critical; the length of the tongue-shaped memberoverhanging the support 21 should be sufficient to prevent slipping ofthe end 20 thereof off the preformed support 21 after the entire hangerassembly and decking are in place and the concrete has been poured. Byway of example, for an inverted channel having a length of about 14inches, and the tongue-shaped member and limiting lug being fabricatedfrom relatively heavy steel of about X 1% inches, the horizontaldistance from the end 20 of the tongue-shaped member and the outersurface of the vertical portion 26 of the lug can be 1% inches.

As shown in FIGS. 4 and 5, a cylindrical pivoting lug 29 is fixedlyattached, as by welding, across the width of that portion of the innersurface of the tongueshaped member 19 disposed within the invertedchannel l0 and immediately adjacent slot 23, whereby the tongue-shapedmember 19, all of lug assembly 26-26a, and pivoting lug 29 pivotallymove or rotate as a unit. A removable locking pin 30 is loosely fittedthrough openings 31 in sides 12 of the inverted channel to prevent suchrotational or pivoting movement until necessary, as described later.

Lug assembly 26-26a performs several functions. First, the verticalportion 26 serves to bear laterally against the preformed support 21,and to define the limiting distance at which the downwardly curved end20 of the tongue-shaped member rests on the preformed support. Second,the portion 26a, angled as shown toward the portion of the tongue-shapedmember 19 disposed within channel and welded to said member at its lowerend 28, cooperates with said member and locking pin 30 to permit thelatter to prevent substantial movement, particularly rotation, of thetongue-shaped member while the locking pin is in place. Third, lugassembly 26-26a absorbs and distributes the stresses upon thetongue-shaped member when the latter is in locked position, locking pin30 also assisting in this function, thus tending to prevent distortionor breaking of the curved portion of the tongueshaped member because ofthe heavy load of joist 13, form decking l4 and concrete 22.

When the hanger device is assembled with supporting joists 13 and formdecks 14 with the locking pin 30 in place, as shown for example in FIG.6, the pivoting lug 29 will bear against the inner surface ofcontinuation 24 of the top 11 of inverted channel 10 immediatelyadjacent the slot 23, as shown in FIG. 4. At the same time, locking pin30 will bear against the inner surface of the angle formed .by thetongue-shaped member 19 and continuation 26a of lug 26 within invertedchannel 10 to prevent movement of the tongue-shaped member and itsintegral lug 26-260. When the locking pin is removed for removing thehanger device after the poured concrete has hardened sufficiently, freeplay of the assembly of the tongue-shaped member and lug 26-26a inrelation to inverted channel 10 is permitted. The downward force thenapplied to channel 10 by reason of its own weight and the weight ofjoist 13 causes pivoting lug 29 to continue to bear against the innersurface of continuation 24 of channel 10 but to roll along said surfacefrom a position immediately adjacent slot 23 in a direction displacedhorizontally therefrom toward the end of channel 10 away from the joist13. The result is to cause the upper (convex) surface of tongue-shapedmember 19 to be displaced slightly vertically from the contiguoussurface of hardened concrete immediately above it and to pivot thetongue-shaped member out of the hardened concrete without bindingthereto.

Pivoting lug 29 performs an important function in the removal operationof the hanger device of the invention from the hardened concrete becauseit translates the downward movement of channel 10 into rotationalmovement of tongue-shaped member 19 out of the concrete. As has beenindicated, the portion of the tongue-shaped member protruding abovechannel 10 is curved to define an arc which is substantially a segmentof the circumference of a circle, such as a quarter of a circle. Therelationship between the cross-sectional diameter of cylindricalpivoting lug 29 and the radius of curvature of the described portion ofthe tongueshaped member protruding above the top of channel It) is alsoimportant to successful removal of the tongueshaped member from thehardened concrete. As has been described, upon removal of locking pin30, pivoting lug 29 rolls along the inner surface of continuation 24 andprovides a migrating center of rotation for the tongue-shaped member. lfthe cross-sectional diameter of lug 29 is too small in relation to theradius of curvature of the portion of the tongue-shaped memberprotruding through and above the top of channel 10, the tongue-shapedmember will not be withdrawn completely from the,hardened concrete. Ifthe diameter of lug 29 is too large in relation to the radius ofcurvature of the described portion of the tongue-shaped member, rotationof the tongue-shaped member will be excessive, causing binding of theupper surface of the tongue-shaped member against the overlyingconcrete. Therefore, the ratio of the diameter of lug 29 to the radiusof curvature of the described portion of the tongue-shaped member mustbe sufficiently large to rotate the tongue-shaped member completely outof the hardened concrete but not so large that binding against theconcrete occurs. From the above and the following description, a desiredratio sufficient to rotate the tongue-shaped member completely out ofthe hardened concrete will be apparent to those skilled in the art.

The radius of curvature of the described portion of the tongue-shapedmember, particularly when considering the sub-portion between thedownwardly curved end 20 thereof and the outer surface of the verticalportion 26 of the position limiting lug, is relatively large so as toresult in almost horizontal movement of the tongue-shaped member out ofthe hardened concrete. It is to be noted, however, that such movement isnot entirely horizontal, experience having shown that the small amountof hardened concrete 32 formed between the top of joist 21 and the innersurface of the tongue-shaped member, which is thin and weak, is manytimes left intact but sometimes may be readily and easily broken duringwithdrawal of the tongue-shaped member from the space it has formed inthe concrete. As noted above, the radius of curvature of the portion ofthe tongue-shaped member embedded in the concrete is so correlated withthe cross-sectional diameter of pivoting lug 29 as to permit theabovedescribed slight vertical displacement and pivoting of thetongue-shaped member completely out of the hardened concrete withoutbinding. By way of example, for a hanger device of the dimensionspreviously given, the above-mentioned radius of curvature of thetongue-shaped member is 1% inches and the cross-sectional diameter ofthe cylindrical pivoting lug is k inch.

For the purpose of further facilitating withdrawal of the tongue-shapedmember, it is desirable, but not essential, slightly to taper a portionof the tongue-shaped member between the downwardly curved end 20 thereofand the outer surface of the vertical portion 26 of the positionlimiting lug.

The apparatus of the present invention severs the adhesive bond betweenthe upper surface of tongueshaped member 19 and the contiguous overlyingconcrete 22 by applying two components of stress against such bond. Thefirst component is a downward tensile stress and the second is a torqueor shearing stress. These two stress components are applied concurrentlyagainst the bond and tend to cooperate in fracturing the bond. Therotational (torque) or shearing stress is a highly advantageous featureof the present invention since shearing forces are especially effectivein fracturing adhesive bonds between unlike materials. Of course, thesesame stresses also apply to that portion 32 of the hardened concretecontiguously underlying the inner (concave) or lower surface oftongue-shaped member, although here the tensile stress component is inan upward direction. However, as has been noted earlier, lay 32 of thehardened concrete is thin and weak and may be easily fractured at timesduring withdrawal of the tongue-shaped member.

Reference has been made to continuation 24 of the top 11 of invertedchannel 10. As stated, continuation 24 forms part of a hanger devicespacing assembly attached to the sides 11 of the inverted channel. Suchassembly itself is an inverted channel having vertical sides 32 integralwith top 24 and horizontal flanges 33 integral with sides 32. The entireassembly is attached, as by welding, to the sides 12 of the invertedchannel where the top 11 thereof ends.

The invention will now be described with reference to its use in forminga concrete structural slab, such as a roof or floor. First, a joist 13of suitable size and length is fitted into two of the hanger devicesdescribed above, one at each end of each joist, and the clamping plates17 are fastened to hold the joist firmly in place. As will be apparent,the joist is not inserted so far into channel as to interfere withmovement of the tongue-shaped member. Depending upon the span of theconcrete slab to be formed, several joist and hanger device assembliesare employed. For example, spans of 8 to 10 feet can be employed, andthe spacing between joist centers may vary from 16 to 32 inches.

Each joist and hanger device assembly is then positioned on thepreformed supports 21 for the concrete slab to be formed, the hanger andjoist assembly resting on the preformed supports at each end of thehanger device at downwardly curved ends 20. At this point is isdesirable to ascertain that all locking pins are firmly in place. Sinceseveral joist and hanger device assemblies are employed, it is alsodesirable to space them equidistantly from each other to distribute theload of concrete evenly. To this end, wooden spacer strips 34, forexample 2 X 2 or 2 X 4 inch, of equal length are placed on flanges 33 ofthe hanger devices and the hanger device and joist assemblies are firmlyfitted against the ends of the spacer strips. Next, wooden spacer stripsare placed between each protruding tongue-shaped member 19 to assure asubstantial continuity of the poured concrete slab between those membersand to eliminate the work required for cutting appropriate spacingeither in the continuous strip 36, to be described, or in the form deck14. These strips 35 may have a thickness of 1 inch, a width equal to thehorizontal distance between the edge of the outer surface of thevertical portion 26 of the position limiting lug abutting preformedsupport 21 and the outermost edge of the portion of the tongue-shapedmember 19, protruding above channel 10, and a length sufficient to fitsnugly against each tongue-shaped member and limiting lug assembly.Continuous wooden strips 36 are then placed snugly abutting strips 35.The width of strips 36 is desirably sufficiently less than the width ofstrips 34 to allow the edge of form decking 14, which may be inchplywood, to rest on spacer strips 34 and permit nailing of the deckingthereto if necessary. It will be apparent that strips 36 can be omitted,if desired, by merely widening decking l4. Desirably, the thickness ofthe strips 34, 35 and 36 in relation to the position of horizontalflanges 33 on the hanger device is such as to leave a small distance oroffset 37, on the order of inch or so, between the top surface of thepreformed support 21 and the top surface of strips 35 and 36. In thismanner, after the concrete slab has been poured and has hardened,relative movement of the slab and preformed supports is prevented.

After the form decking 14 is put into place, the entire assembly ofspacer strips and form decking is secured in place by nailing, using asfew and as small nails as possible. Desirably, nailing should beconfined to securing strips 35 and 36 to strip 34, nailing of theplywood decking to strip 34 being required only when a severely warpedplywood sheet is used as decking.

It will be apparent to those skilled in the art that the assembliesdescribed and shown, for example, in FIG. 6 are duplicated on the otherside of the preformed support 21 and as many times as necessary withother preformed supports to provide a unitary concrete slab spanning asmany such supports as required and as may be limited in area and span bythe particular job under construction.

After the desired number of assemblies are in place, concrete is pouredand allowed to harden to form the structural slab. After the concretehas reached its required strength, each hanger device-supporting joistassembly is ready to be removed. To accomplish this, locking pin 30 isfirst removed, if necessary by knocking it out. If the channel and joistassembly does not begin to lower because of its weight when the pin isremoved, a sharp downward rap and pull may be applied to clamping plate17. In either case, as the above downward force is applied to the hangerdevice in the vicinity of the tongue-shaped member 19, that member willdrop slightly and pivot out of the hardened concrete as previouslydescribed. Normally, as the one end of the hanger device is removed fromthe hardened concrete, continued lowering of the hanger device-joistassembly will cause rotation out of the concrete of the tongue-shapedmember of the hanger device at the other end of the joist withoutremoval of the locking pin. However, if joist lengthor an obstructionprevents sufficient rotation of the tongue-shaped member at such otherend, removal of the locking pin and the other procedure described aboveis followed.

The hanger device of this invention permits the pouring of concretestructural slabs having a thickness of 4% or more inches spanning 8 to10 or more feet between supports, although it may, of course, be usedfor thinner slabs of considerably smaller span. It eliminates the costlyshoring, wedging and nailing required for form decks for such thickslabs, along with the labor costs required to erect and remove them. Inaddition to the above savings of lumber and scaffolding, the hangerdevice of this invention has the advantage of being readily removed fromhardened concrete without binding and is capable of repeated reusedespite any roughness of the surface metal of the portion of thetongue-shaped member protruding above the inverted channel, or build-upof concrete film thereon.

What is claimed is:

1. An apparatus useful in conjunction with a preformed support and formdecking for pouring a substantially horizontal concrete structural slabsupported by said preformed support, comprising:

support means for holding a joist for supporting said form decking,

said support means having inner and outer surfaces and a slot adjacentone end thereof,

a movable tongue-shaped member carried by said support means andprotruding through said slot above and below the top of said supportmeans, the portion of said tongue-shaped member protruding above saidsupport means being curved, defining an. arc which is substantially asegment of the circumference of a circle, and being adapted to rest atits downwardly curved end on said preformed support,

locking means, for preventing movement of said tongue-shaped memberduring pouring of the concrete while the downwardly curved end of saidmember is resting on said preformed support and the curved protrudingsurfaces of said member are being covered by the concrete,

circular pivot means fixed to the portion of said tongue-shaped memberwithin said support means immediately adjacent said slot interiorly ofsaid member, said pivot means being in contact with the inner surface ofsaid support means,

said circular pivot means having a cross-sectional diameter the ratio ofwhich to the radius of curvature of said portion of the tongue-shapedmember protruding above said support means permits rolling migration ofthe circular pivot means along the inner surface of said support meansin a horizontal direction toward the end of said support means and awayfrom said joist upon removal of said locking means,

whereby after said concrete has been poured and has hardened saidtongue-shaped member may be rotated completely out of the hardenedconcrete without binding upon removal of said locking means.

2. The apparatus of claim 1, wherein said support means is an invertedchannel.

3. The apparatus of claim 1, wherein said circular pivot means is acylindrical lug.

4. The apparatus of claim 1 wherein a position limiting lug is attachedat its upper end to said curved protruding portion of the tongue-shapedmember and at its lower end to that end of the tongue-shaped memberwithin said support means.

5. An apparatus useful in conjunction with a preformed support and formdecking for pouring a substantially horizontal concrete structural slabsupported by said preformed support, comprising:

an inverted channel having a slot in its top adjacent one end thereof,

said inverted channel being adapted to hold a joist for supporting saidform decking,

a movable tongue-shaped member carried by said inverted channel andprotruding through said slot above and below the top of said invertedchannel,

the portion of said tongue-shaped member protruding above said invertedchannel being curved and having a downwardly turned end defining an arcwhich is substantially a quarter segment of the circumference of acircle, and being adapted to rest at its downwardly curved end on saidpreformed support,

the portion of said tongue-shaped member protruding below the top ofsaid inverted channel having an end terminating within said channel,

a position limiting lug having a vertical portion which is attached atits upper end to the portion of said ton ue-sha ed member rotrudin abovsaid invered chari nel at aboutt e mldpo tlon of the concave surface ofsaid tongue-shaped member,

the remaining portion of said position limiting lug being angled toward,and being attached at its lower angled end to, that end of saidtongueshaped member terminating within said inverted channel,

locking means formed by a removable locking pin in contact with thesurfaces of the angle formed by the end of said tongue-shaped member andthe end of the position limiting lug attached thereto within saidinverted channel,

a cylindrical pivoting lug attached across the width of that portion ofsaid tongue-shaped member within said inverted channel and immediatelyadjacent said slot,

said cylindrical pivoting lug bearing on the inner surface of the top ofsaid inverted channel,

said cylindrical pivoting lug having a cross-sectional diameter theratio of which to the radius of curvature of said portion of saidtongue-shaped member protruding above said inverted channel permitsrolling migration of the cylindrical pivoting lug along said innersurface of the top of the inverted channel in a horizontal directiontoward the end of said inverted channel and away from said joist uponremoval of said locking pin,

whereby after said concrete has been poured and has hardened saidtongue-shaped member may be rotated completely out of the hardenedconcrete without binding.

1. An apparatus useful in conjunction with a preformed support and formdecking for pouring a substantially horizontal concrete structural slabsupported by said preformed support, comprising: support means forholding a joist for supporting said form decking, said support meanshaving inner and outer surfaces and a slot adjacent one end thereof, amovable tongue-shaped member carried by said support means andprotruding through said slot above and below the top of said supportmeans, the portion of said tongue-shaped member protruding above saidsupport means being curved, defining an arc which is substantially asegment of the circumference of a circle, and being adapted to rest atits downwardly curved end on said preformed support, locking means forpreventing movement of said tongue-shaped member during pouring of theconcrete while the downwardly curved end of said member is resting onsaid preformed support and the curved protruding surfaces of said memberare being covered by the concrete, circular pivot means fixed to theportion of said tongue-shaped member within said support meansimmediately adjacent said slot interiorly of said member, said pivotmeans being in contact with the inner surface of said support means,said circular pivot means having a cross-sectional diameter the ratio ofwhich to the radius of curvature of said portion of the tongue-shapedmember protruding above said support means permits rolling migration ofthe circular pivot means along the inner surface of said support meansin a horizontal direction toward the end of said support means and awayfrom said joist upon removal of said locking means, whereby after saidconcrete has been poured and has hardened said tongue-shaped member maybe rotated completely out of the hardened concrete without binding uponremoval of said locking means.
 2. The apparatus of claim 1, wherein saidsupport means is an inverted channel.
 3. The apparatus of claim 1,wherein said circular pivot means is a cylindrical lug.
 4. The apparatusof claim 1 wherein a position limiting lug is attached at its upper endto said curved protruding portion of the tongue-shaped member and at itslower end to that end of the tongue-shaped member within said supportmeans.
 5. An apparatus useful in conjunction with a preformed supportand form decking for pouring a substantially horizontal concretestructural slab supported by said preformed support, comprising: aninverted channel having a slot in its top adjacent one end thereof, saidinverted channel being adapted to hold a joist for Supporting said formdecking, a movable tongue-shaped member carried by said inverted channeland protruding through said slot above and below the top of saidinverted channel, the portion of said tongue-shaped member protrudingabove said inverted channel being curved and having a downwardly turnedend defining an arc which is substantially a quarter segment of thecircumference of a circle, and being adapted to rest at its downwardlycurved end on said preformed support, the portion of said tongue-shapedmember protruding below the top of said inverted channel having an endterminating within said channel, a position limiting lug having avertical portion which is attached at its upper end to the portion ofsaid tongue-shaped member protruding above said inverted channel atabout the midportion of the concave surface of said tongue-shapedmember, the remaining portion of said position limiting lug being angledtoward, and being attached at its lower angled end to, that end of saidtongue-shaped member terminating within said inverted channel, lockingmeans formed by a removable locking pin in contact with the surfaces ofthe angle formed by the end of said tongue-shaped member and the end ofthe position limiting lug attached thereto within said inverted channel,a cylindrical pivoting lug attached across the width of that portion ofsaid tongue-shaped member within said inverted channel and immediatelyadjacent said slot, said cylindrical pivoting lug bearing on the innersurface of the top of said inverted channel, said cylindrical pivotinglug having a cross-sectional diameter the ratio of which to the radiusof curvature of said portion of said tongue-shaped member protrudingabove said inverted channel permits rolling migration of the cylindricalpivoting lug along said inner surface of the top of the inverted channelin a horizontal direction toward the end of said inverted channel andaway from said joist upon removal of said locking pin, whereby aftersaid concrete has been poured and has hardened said tongue-shaped membermay be rotated completely out of the hardened concrete without binding.